The present invention relates to topical adhesives for attachment to the skin. In particular the present invention relates to such topical adhesives which can be employed for attachment to the skin, particularly for the adhesion of protective articles such as genital-, knee- or elbow-protectors or bandages; clothing such as bras, surgical gowns, or parts of garments during fitting at a tailor; nasal plasters; prosthesis such as breast replacements or wigs; heat wraps, pads, and/or packs, e.g. for topical relief of pain or simply to provide warmth; cold wraps e.g. to provide pain relieve from bruises and to reduce swelling; hearing aids; protective face masks; ornamental articles such as jewelry, earrings, guises, tattoos; goggles or other eye wear. The topical adhesive provides secure attachment and is pleasing to the skin upon application, yet causes no discomfort and a low level of adhesive residues on the skin upon removal. This is achieved by selecting the chemical composition and rheological characteristics of the topical adhesives, in particular with reference to the relationship between the elastic modulus Gxe2x80x2 and the viscous modulus Gxe2x80x3 of the topical adhesive.
The general prior art in the field of topical adhesives for attachment to the skin is particularly developed in the field of band-aids, plasters and bandages. These articles are, however, typically applied in an emergency situation where for example a cut into the skin of the wearer has occurred and absorption of the body liquids emanating from a wound is desired. In this context performance aspects of the absorbent article such as comfortable and easy use and application, painless removal, discreteness are subordinate to criteria such as sterility, healing support, mechanical protection of the wound. Also such wound covering absorbent articles are mostly adhered to skin areas where prior to application of the absorbent article body hair can be removed or where little or no hair grows.
The present invention relates to topical adhesives which are particularly useful to protective articles such as genital-, knee- or elbow-protectors or bandages; clothing such as bras, surgical gowns, or parts of garments during fitting at a tailor; nasal plasters; prosthesis such as breast replacements or wigs; heat wraps, pads, and/or packs, e.g. for topical relief of pain or simply to provide warmth; cold wraps e.g. to provide pain relieve from bruises and to reduce swelling; hearing aids; protective face masks; ornamental articles such as jewelry, earrings, guises, tattoos; goggles or other eye wear. Such articles are not used for absorption of body liquids. For example attachment of a wig to the skin on the skull or of elbow and knee protectors to these surfaces of the body which undergo substantial extending and wrinkling can suitably be done by the adhesive of the present invention.
Topical adhesives that are used for absorbent articles such as sanitary napkins or pantiliners have generally been disclosed in U.S. statutory invention registration H1602 or WO 96/33683. Some more details of the adhesive have been disclosed in PCT application WO 95/16424. In this document sanitary articles having a topical adhesive which is applied on the wearer facing side of a sanitary napkin along the entire periphery are disclosed. The problem underlying this document is primarily the safe attachment to the skin but mentions also the problems of detachment of such articles after use without causing undue pain to a wearer.
The disclosure of WO 95/16424 includes a detailed analysis of the criteria for the topical adhesive in respect to rheological criteria. However, this document has little regard to the problem of painless removal of such articles since the rheological criteria taught include epilatory, i.e. hair removal, compositions which are commercially available such as STREP MIELE (TM) sold in Italy by Laboratori Vaj S.p.A. The adhesives for topical attachment mentioned in WO 95/16424 include also today""s pressure sensitive adhesives which are used to attach sanitary napkins to undergarments. Further, this document only identifies static rheological characteristics but is silent as to the dynamic rheological behaviour of a topical adhesive.
In WO 96/13238 a frequency dependent topical adhesive model is disclosed. However, all measurements disclosed, e.g. on page 9, were made at temperatures between xe2x88x9260xc2x0 C. and +120xc2x0 C. and at actual frequencies of 0.1 to 100 rad/s. In order to obtain the necessary data at application temperature (about 20xc2x0 C., typical bath room, i.e. storage temperature) the Williams-Landel-Ferry (hereinafter WLF) equation was used.
This WLF equation is empirical and only valid within certain limits e.g. it cannot be used to extrapolate to temperatures below the glass transition temperature of a polymeric adhesive also the WLF cannot be used on the basis of values obtained below the glass transition temperature. Details about the WLF equation and its applicability can be found in xe2x80x9cPrinciples of Polymer processingxe2x80x9d by Z. Tadmor and C. G. Gogos, published by John Wiley and Sons or in xe2x80x9cViscoelastic Properties of Polymersxe2x80x9d by J. D. Ferry also published by John Wiley and Son. Since this is already missing from WO 96/13238 the applicability of the disclosed data cannot be assessed.
European Patent Application EP-638 303 discloses the use of a topical adhesive on side cuffs of sanitary napkins in order to keep the cuffs in an upright position. Swiss publication CH-643730 discloses the use of a very long sanitary napkin having chamfered outer edges with a topical adhesive at the four corners of the outer edges in order to provide a topical adhesive area well outside the region of pubic hair growth. Both applications are silent as to the adhesive composition.
Based on the above state of the art it is an objective of the present invention to provide a topical adhesive for secure attachment and painless removal from the skin, combined with a reduced amount of residual adhesive that remains on the skin or on the hairs after removal of the topical adhesive composition, for articles outside the absorbent article field.
It is yet a further objective of the present invention that the adhesive for topical attachment does not cause a cold or otherwise unacceptable temperature sensation upon application despite a temperature difference of the adhesive in respect to the skin temperature.
In addition to the above objectives of the present invention it is also desirable for topical adhesives to provide additional benefits such as delivery/dispersal of a compound or composition which is beneficial for the skin or for the body in general. Further, topical adhesives which do not affect the natural skin condition, e.g. by being breathable or water vapour transmitting, are preferred.
The present invention relates to topical adhesives which are particularly useful to protective articles such as genital-, knee- or elbow-protectors or bandages; clothing such as bras, surgical gowns, or parts of garments during fitting at a tailor; nasal plasters; prosthesis such as breast replacements or wigs; heat wraps, pads, and/or packs, e.g. for topical relief of pain or simply to provide warmth; cold wraps e.g. to provide pain relieve from bruises and to reduce swelling; hearing aids; protective face masks; ornamental articles such as jewelry, earrings, guises, tattoos; goggles or other eye wear. Such articles are not used for absorption of body liquids. For example attachment of a wig to the skin on the skull or of elbow and knee protectors to these surfaces of the body which undergo substantial extending and wrinkling can suitably be done by the adhesive of the present invention.
Detailed analysis of the sequence of common situations occurring from the application of such articles to the time of removal has shown that specific adhesive characteristics need to be satisfied in order to achieve the desired performance objectives, in particular secure initial attachment, secure attachment during use, painless removal at the end and a reduced level of adhesive residues on the skin after removal. The characteristics which have been considered in this context are the elastic modulus describing the elastic behaviour of the material and the viscous modulus which describes the viscous behaviour of the adhesive material.
The viscous behaviour of the adhesive can be interpreted to represent an indication of the ability of the adhesive to quickly attach and securely adhere. The elastic behaviour can be interpreted as an indication of the xe2x80x9chardnessxe2x80x9d behaviour of the adhesive. Its value is also critical for good initial attachment. Their combination is believed to be an indicator of the required force upon removal. The relation between elastic and viscous modulus is considered to be an indication on which fraction of the removal energy will be dissipated within the adhesive and which fraction is available to trigger the actual removal. The relation between the elastic and viscous modulus also gives an indication of the internal cohesiveness of the adhesive, which is in turn related to the possible presence of adhesive residues on the skin after removal of the topical adhesive composition.
In order to provide topical adhesives for secure initial and prolonged attachment and easy/painless removal the relation between the elastic modulus and the viscous modulus as well as their dynamic behaviour is of key importance.
The topical adhesive has an elastic modulus at a temperature of 37xc2x0 C. (100xc2x0 Fahrenheit) abbreviated Gxe2x80x237 and a viscous modulus at a temperature of 37xc2x0 C. (100xc2x0 Fahrenheit) of Gxe2x80x337. The difference xcex94(Gxe2x80x237xe2x88x92Gxe2x80x337) between the elastic modulus Gxe2x80x237 at a frequency of 1 rad/sec and the viscous modulus Gxe2x80x337 at a frequency of 1 rad/sec is also defined for the topical adhesive. This difference gives an indication of the behaviour of the topical adhesive with respect to the level of adhesive residues left on the skin after removal of the topical adhesive. The adhesive further has a dynamic elastic behaviour defined as xcex94Gxe2x80x237 which is the difference of Gxe2x80x237 at a frequency of 100 rad/sec and Gxe2x80x237 at a frequency of 1 rad/sec and a dynamic viscous behaviour xcex94Gxe2x80x337 which is the difference of Gxe2x80x337 at a frequency of 100 rad/sec and Gxe2x80x337 at a frequency of 1 rad/sec.
The topical adhesive according to the present invention satisfies the following conditions:
the difference xcex94(Gxe2x80x237xe2x88x92Gxe2x80x337) (1 rad/sec) is greater than or equal to 1250 Pa, preferably greater than or equal to 2500 Pa, more preferably greater than or equal to 3500 Pa.
Further preferred conditions are:
the value of the ratio Gxe2x80x237/Gxe2x80x337 at least for the frequency range from above 1 rad/s up to 100 rad/s should preferably be 3.3 or above, more preferably 5 or above, most preferably 10 or above, while not exceeding about 30, preferably 20, anywhere in the frequency interval.
the rheological behaviour can also be related to the values of the Glass Transition Temperature Tg. For topical adhesives according to the present invention Tg should preferably be less than xe2x88x9215xc2x0 C., more preferably less than xe2x88x9220xc2x0 C. and most preferably less than xe2x88x9225xc2x0 C.
the rheological behaviour and acceptance of a topical adhesive can also be related to the specific heat capacity. Preferably the specific heat capacity of the topical adhesive is less than 4 J/g/K, more preferably less than 3 J/g/K and most preferably less than 2 J/g/K.
the rheological behaviour and acceptance of a topical adhesive can also be related to the specific heat conductivity of the adhesive. Preferably the specific heat conductivity is as low as possible, preferably between 1 and 0.1 W/m/K, most preferably between 0.6 and 0.1 W/m/K. However, even though these ranges allow selection of appropriate adhesives, in the case of heat or cold wraps it is desirable to have a relatively high value of heat conductivity to support the function of such articles.
Adhesive compositions which satisfy the above criteria can be used as topical adhesives for the above mentioned articles provided they also satisfy the common requirements of being safe for use on human or animal skin during use and generally after disposal of the article.
Often the criteria of hygienic appearance and pleasant feel upon contact are important such that adhesive composition which are transparent or white, and which prevent a cold, unpleasant feeling upon application are preferred.
The above rheological criteria and other considerations can be satisfied by adhesive compositions where the composition comprises from 45%, preferably from 51%, to 99.5% of a plasticising compound or composition which is liquid at 20xc2x0 C., from 0.5 to 20%, preferably 5% to 15%, of a polymeric compound or composition which is soluble or swellable in the plasticising compound or composition and with a tackifying resin in an amount in the range from 0% to 50% by weight of the composition, preferably from 0% to 600% by weight of the polymeric compound. The plasticising compound or composition is preferably selected from the group consisting of water, alcohols (preferably glycerol), glycols, polyglycols, liquid polybutenes, oil or combinations thereof. The polymeric compound or composition is preferably selected from the group consisting of block-copolymer-thermoplastic-elastomers, styrene-block-copolymers and hydrogenated styrene-block-copolymers, polyacrylics, polyvinyl alcohol, natural gum or gelatines, polyethyleneoxide, polyvinylpyrrolidon (PVP), polyvinylethers, cellulose derivatives, or combinations thereof.